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Abstract

Introduction

Extracorporeal circulation induces hemostatic alterations that lead to inflammatory
response (IR) and postoperative bleeding. Tranexamic acid (TA) reduces fibrinolysis
and blood loss after cardiopulmonary bypass (CPB). However, its effects on IR and
vasoplegic shock (VS) are not well known and elucidating these effects was the main
objective of this study.

Methods

A case control study was carried out to determine factors associated with IR after
CPB. Patients undergoing elective CPB surgery were randomly assigned to receive 2
g of TA or placebo (0.9% saline) before and after intervention. We performed an intention-to-treat
analysis, comparing the incidence of IR and VS. We also analyzed several biological
parameters related to inflammation, coagulation, and fibrinolysis systems. We used
SPSS version 12.2 for statistical purposes.

Results

In the case control study, 165 patients were studied, 20.6% fulfilled IR criteria,
and the use of TA proved to be an independent protective variable (odds ratio 0.38,
95% confidence interval 0.18 to 0.81; P < 0.01). The clinical trial was interrupted. Fifty patients were randomly assigned
to receive TA (24) or placebo (26). Incidence of IR was 17% in the TA group versus
42% in the placebo group (P = 0.047). In the TA group, we observed a significant reduction in the incidence of
VS (P = 0.003), the use of norepinephrine (P = 0.029), and time on mechanical ventilation (P = 0.018). These patients showed significantly lower D-dimer, plasminogen activator inhibitor
1, and creatine-kinase levels and a trend toward lower levels of soluble tumor necrosis
factor receptor and interleukin-6 within the first 24 hours after CPB.

Conclusion

The use of TA attenuates the development of IR and VS after CPB.

Trial registration number

ISRCTN05718824.

Introduction

Cardiopulmonary bypass (CPB) may activate an inflammatory response (IR) involving
contact system, complement, cytokine, and coagulation-fibrinolytic cascades, among
others. The coagulation-fibrinolytic cascades and the IR, though in many respects
separate processes, are closely interconnected [1]. Several preoperative and perioperative risk factors for IR have been proposed [2,3]. The incidence of vasoplegic shock (VS), the most severe presentation of IR, may
be as high as 10% [4].

Numerous strategies to reduce IR and bleeding in high-risk patients exist, among which
is the use of aprotinin [5]. Like aprotinin, tranexamic acid (TA) inhibits fibrinolysis (that is, plasmin activity
and D-dimer formation), but its effect on IR remains unclear. Additionally, there
is evidence that fibrinolysis is a marker for the onset of systemic inflammation.
[6].

This paper describes a study in two parts. First, we performed a case control study
to determine risk factors associated with IR in patients who underwent CPB. Second,
we carried out a randomized, double-blind, placebo-controlled study to test the hypothesis
that inhibition of excessive fibrinolysis by TA could reduce the incidence of IR and
VS after CPB. The second study was interrupted because of the high incidence of adverse
effects observed in the placebo group. Thus, we present data of an interim analysis.

Materials and methods

The study was approved by the institutional ethics committee of the University Hospital
of the Canary Islands (La Laguna, Spain) and was conducted according to the Declaration
of Helsinki. The study consisted of two parts.

Part 1: Assessment of postoperative incidence and protective/risk factors for inflammatory
response after cardiopulmonary bypass

After obtaining informed written consent, we prospectively enrolled 191 consecutive
Caucasian adult patients scheduled for cardiac surgery with CPB between January 2002
and February 2003. To avoid the effect of confounding factors on the IR, patients
with endocarditis and those admitted with cardiogenic shock or with intra-aortic counterpulsation
balloon were excluded (n = 26). Finally, a total of 165 patients were included. No patients received perioperative
anti-inflammatory agents such as corticosteroids or nonsteroidal anti-inflammatory
drugs.

IR was clinically defined as a core body temperature of greater than 38°C (100.4°F)
in the first 4 hours after intervention, a systemic vascular resistance index of less
than 1,600 dyn-seconds/cm5 per square meter, and a cardiac index of greater than 3.5 L/minute per square meter.
VS was defined as persistent hypotension (mean arterial pressure of less than 70 mm
Hg) requiring norepinephrine for at least 4 hours after failure to respond to appropriate
volume expansion (pulmonary capillary wedge pressure of greater than 15 mm Hg). Serum
concentrations of interleukin-6 (IL-6) were measured at 4 hours after CPB (Materials
and methods, part 2). Risk factors associated with IR after CPB, including demographic
variables, comorbid conditions, preoperative medication, duration of CPB, aortic crossclamp
time, and the use of antifibrinolytic drugs, were investigated. Perioperative management
of the groups was similar in the two studies (Materials and methods, part 2), except
for the study medication. In this study, the surgeon decided when to use TA.

We performed a randomized, double-blind, placebo-controlled study with consecutive
Caucasian adult patients undergoing elective CPB surgery from February to May 2004.
Postoperative care of the patients was performed in a 24-bed intensive care unit (ICU)
at a university hospital. We excluded emergency interventions, patients with a history
of chronic coagulopathy (prothrombin time [PT] of less than 50% or international normalized
ratio of greater than 2 and platelets of less than 50,000/mm3 or aggregation dysfunction), renal failure (creatinine of greater than 2 mg/dL), chronic
hepatopathy (Child B or higher degree), use of immunosuppressant drugs, endocarditis,
sepsis in the first 24 hours after intervention, or unwillingness to enroll. Before
CPB, participants had normal bleeding time, platelet collagen/epinephrine and collagen/ADP
closure time, PT, activated partial thromboplastin time, and thrombin time. None of
the patients received anti-inflammatory agents such as corticosteroids or nonsteroidal
anti-inflammatory agents, including acetyl salicylate acid or clopidogrel or immunosuppressants,
on the previous 5 days and the first 24 hours following intervention.

After informed written consent was obtained, patients were randomly assigned by independent
pharmacists using a list of pseudorandomized numbers to receive coded infusions of
either TA or placebo (0.9% saline) with doses of 2 g pre-CPB and post-CPB after protamine
administration (using the same protocol as in the previous part of the study). The
code was revealed once recruitment, data collection, and laboratory analyses were
completed. The primary endpoint was to test the effect of TA on the incidence of IR
and VS in patients undergoing elective CPB. Secondary endpoints were biological parameters
related to inflammation, coagulation, and fibrinolysis systems.

Data collection

Demographic variables, comorbid conditions, perioperative clinical data, and postoperative
outcomes (IR, VS, duration of mechanical ventilation, postsurgical ICU stay and hospital
stay, and mortality) were recorded. Core body temperature, biochemical determinations
(hematology, inflammation, coagulation, and fibrinolysis), and hemodynamic parameters
were recorded before intervention (baseline), on admission to the ICU after surgery
(0 hours), and at 4 hours and 24 hours after intervention. In addition, blood loss
measured by tube chest drainage and the amount of hemoderivatives used, as well as
its frequency, were collected after intervention at the above time points and when
chest tubes were removed (defined as total bleeding). Surgical risk was calculated
by Parsonnet score.

Anesthetic procedures were standardized and consisted of an opioid-based anesthetic
supplemented with volatile anesthetic and muscle relaxants. All interventions were
performed by the same surgical team with wide experience in these surgical interventions.
All patients were preoperatively monitored with a pulmonary artery continuous thermodilution
catheter (Edwards Lifesciences LLC, Irvine, CA, USA). Neither heparin-coated circuits
nor leukocyte filters were used. The extracorporeal circuit consisted of a hardshell
membrane oxygenator (Optima XP; Cobe, Denver, CO, USA, or Quantum Lifestream International,
Inc., Woodlands, TX, USA), a Tygon™ (Dideco s.r.l., Mirandola, Italy) extracorporeal
circuit, and a Medtronic™ Biopump (Medtronic, Inc., Minneapolis, MN, USA) centrifugal
pump. Below hypothermic temperatures of 28°C to 30°C, the pump flow was adjusted to
maintain a mean arterial pressure of greater than 60 mm Hg and a flow index of 2.2
L/minute per square meter. Myocardial protection was achieved using antegrade, cold,
St. Thomas 4:1 sanguineous cardioplegia. The circuit was primed with 30 mg of heparin
followed by an initial dose of 3 mg/kg and further doses when necessary to achieve
and maintain an activated clotting time of 480 seconds. To reverse the effect of heparin,
protamine was used based on blood heparin levels measured by Hepcon® (Medtronic, Inc.). A blood salvage device was used in all patients. The transfusion
trigger was a hemoglobin threshold of less than 8 g/dL, PT of less than 50%, and platelets
of less than 50,000/mm3. Fluid management was carried out to achieve 8 to 12 mm Hg of central venous pressure
or 12 to 15 mm Hg of pulmonary artery occlusion pressure at zero positive end-expiratory
pressure by infusions of crystalloids and colloids. Catecholamine support, when necessary,
was used as follows: Norepinephrine was titrated to achieve a mean arterial pressure
of greater or equal to 70 mm Hg, and dobutamine was titrated to achieve a cardiac
index of greater or equal to2.5 L/minute per square meter. Amines were tapered off
in steps of 0.02 and 1 μg/kg per minute, respectively.

Statistical analysis

Comparisons between groups (patients with and without IR or the TA group versus placebo
group) were performed using the Pearson χ2 test or Fisher exact test for categorical variables and the Student t test or the Mann-Whitney U test for continuous variables, as appropriate. Logistic regression analysis (forward
stepwise conditional) was used to identify independent risk factors associated with
IR. Initially, only variables with a P value of less than 0.15 (TA, clamping time, and mixed cardiac surgery) in the univariate
analysis were incorporated. To perform the controlled study, a sample size of 100
patients was required to detect a statistically significant reduction of at least
20% in IR by TA. Assuming an incidence of 30% in the placebo group, a study population
of 100 patients was expected to have 80% power to detect a 20% reduction in IR. For
primary endpoint outcomes, all differences in preoperative variables with a P value of less than 0.15 in the univariate analysis of the controlled study were entered
into a logistic regression analysis. Results for qualitative variables are expressed
as frequency and percentage. Quantitative variables are expressed as mean ± standard
deviation or as median and interquartile range in the case control study and as mean
and 95% CI in the controlled study. A P value of less than 0.05 was considered statistically significant. For primary endpoint
outcomes of the controlled study, exact P values are reported. SPSS version 12.2 (SPSS Inc., Chicago, IL, USA) was used.

Results

Part 1: Assessment of postoperative incidence and protective/risk factors for inflammatory
response after cardiopulmonary bypass

Table 1 shows demographic and clinical data of patients who developed IR as compared with
those without IR. The only significant difference in the univariate analysis was the
use of TA, which was associated with a lower incidence of IR (P = 0.002). IR was found in 26 (33%) of 79 patients who did not receive TA versus 8
(9%) of 86 patients who received TA. Initially, we included aortic clamping time (P = 0.11), mixed cardiac surgery (P = 0.05), and TA administration (P < 0.01). Only the use of TA proved to be an independent protective variable (odds
ratio [OR] 0.38, 95% confidence interval [CI] 0.18 to 0.81; P = 0.009).

Twenty (12%) of the 165 patients presented VS. In the non-TA group, 16 (20%) out of
79 patients developed VS. As expected, patients with IR were more likely to develop
VS (58% versus 0%; P < 0.001). There were 3 deaths (1.8%) in the whole group; none of them had developed
IR.

The study was interrupted by the ethics committee after the inclusion of 50 patients
due to the higher proportion of severe bleeding observed in the placebo group during
follow-up. The primary analysis was intention-to-treat and involved all patients who
were randomly assigned. We studied 50 patients, 24 receiving TA and 26 placebo, from
68 consecutive patients, of whom 18 met criteria for exclusion (5 off-pump, 2 with
previous surgery coagulation disorders, 5 surgical emergencies, 1 Jehovah's Witness,
4 with endocarditis, and 1 with chronic renal failure on hemodialisis) (Figure 3). Demographic variables, comorbidity, medical treatment, preoperative biochemical
data, and surgical procedures were similar in the two groups (Table 2).

The incidence of IR was significantly lower in the TA group (17%) than in the placebo
group (42%) (P = 0.047). TA showed a protective effect for IR (OR 0.1, 95% CI 0.01 to 0.7) after
adjusting for Parsonnet score, aortic clamping time, and type of surgery. As compared
with the TA group, the relative risk for developing IR was 2.47 for the placebo group
(97.5% CI 1.1 to 5.7). The absolute risk difference was 25%. Thus, the number needed
to treat to reduce IR was 4 patients (97.5% CI 2 to 20 patients). The incidence of
VS was 0% in the TA group versus 23% in the placebo group (P < 0.001).

The TA group had significantly lower 24-hour chest tube bleeding (P < 0.001) (Figure 4) and transfusion requirements before ICU discharge compared with the placebo group.
In addition, the TA group required significantly less vasopressor medication and mechanical
ventilation time. We did not find significant differences in duration of ICU stay
or hospital stay after surgery between groups (Table 3). One patient from the placebo group required reintervention due to nonsurgical bleeding.
There were no deaths in this study.

Table 3 shows the biological variables studied in both groups. Significantly lower D-dimer
(Figure 5), PAI-1, and creatine-kinase levels were observed in patients in the TA group within
the first 24 hours after CPB; lower levels of STNFR and IL-6 were observed in the
TA group, but these differences were not significant. The remaining variables (coagulation
parameters) did not show significant differences (data not shown).

Discussion

Part 1: Assessment of postoperative incidence and protective/risk factor for inflammatory
response after cardiopulmonary bypass

According to previous reports, it is widely accepted that a systemic response is induced
in nearly all patients undergoing open-heart surgery [1]. The occurrence rate of a hyperdynamic state after CPB has been reported to be as
low as 4%. [7] and as high as 44% [8]. Indeed, much of the difference in prevalence may relate to the criteria used to
define the vasodilatory syndrome [9]. The American College of Chest Physicians/Society of Critical Care Medicine consensus
proposed a very sensitive, but very low-specificity, definition for systemic IR syndrome
[10]. This definition is often inappropriate for cardiac surgery patients (mechanically
ventilated, hypothermic, with pacemakers, and so on), and therefore we applied a definition
based on hemodynamic data provided by the latest International Definitions Conference
[11]. Other studies have proposed definitions based on analytical data such as high levels
of IL-6 [12], whose serum concentrations correlate with morbidity and mortality following pediatric
cardiac surgery [13]. The present study has shown that patients who fulfilled clinical criteria also had
higher levels of IL-6. Therefore, the definition used seemed to be suitable to identify
protective or risk factors for IR after CPB, even though this clinical picture may
vary from mild to severe form. IR was found in one fourth of the patients, of whom
more than half developed VS. TA was significantly associated with a lower incidence
of IR. The incidence in those patients who did not receive TA was nearly one third,
similar to other reports [12]. Thus, the next step was to test this hypothesis using an experimental design.

The trial was interrupted by the ethics committee due to the adverse effects (excessive
bleeding) observed in the placebo group during follow-up. Our results indicate that
TA reduces the incidence of IR and VS in CPB patients as well as postoperative bleeding
and hemoderivative requirements. Several mechanisms have been proposed to explain
the development of IR after CPB, such as contact activation, ischemia-reperfusion,
and endotoxemia. These initiating factors may activate numerous systems involving
complement, cytokines, immune cellular response with dysfunction of endothelium, and
alteration of coagulation-fibrinolytic cascades [1]. This activation exposes patients to either immediate risk of major bleeding [14] or IR, as we saw in the first part of the study. The IR in cardiac surgery is closely
related to hemostatic alterations. [15]. In this sense, higher D-dimer and IL-6 levels have been found in CPB patients with
vasoplegic syndrome. [16]. In fact, IR and major bleeding could be considered as final outcomes of the same
triggering stimulus, so that hyperfibrinolysis could play an important role in these
processes. [17,18]. The suppression of excessive plasmin activity or D-dimer formation may play an important
role in the generation of proinflammatory cytokine (IL-6) during and after CPB [5], which has been reported to be involved in circulatory dysregulation and metabolic
derangement [4].

TA, an antifibrinolytic agent. [19], reduces bleeding and transfusion requirements after cardiac surgery. [20,21]. A synthetic derivative of the amino acid lysine, TA exerts its antifibrinolytic
effect through the reversible blockade of lysine-binding sites on plasminogen molecules.
However, the effect of TA on IR during cardiac surgery and CPB has received little
attention [22]. In our study, low levels of D-dimer at all postoperative time points in the TA group
clearly suggest that these patients experienced less secondary fibrinolysis which
leads to reduced postoperative bleeding. Lower levels of PAI-1 at 4 hours may reflect
less previous activation of fibrinolysis with less secondary production. We observed
no striking changes in coagulation and complement parameters in the TA group. However,
STNFR levels and IL-6 levels at 4 hours, which have been implicated in the development
of postoperative morbidity after CPB [23], were lower, as were myocardial enzymes on admission, which may reflect a reduced
IR [24] and thus less perioperative insult. Casati and colleagues [25] have proven that TA can effectively decrease postoperative IL-6 levels in this context.
Blood transfusions are able to alter the IR, including cytokine concentrations of
IL-6. However, we suppose that an influence of transfusions on the postoperative development
of IR can be ruled out by the fact that only three patients were transfused before
setting up the clinical criteria for IR. Furthermore, the number of red blood cell
units given during the first hours of the postoperative period did not differ significantly
between groups. Finally, due to the fact that vasodilator drugs may interact with
vascular resistance, the inclusion of temperature as part of the clinical criteria
rules out the confounding effect of these drugs.

The TA patients needed smaller amounts of vasopressors and shorter duration of mechanical
ventilation. Greater bleeding may lead to higher doses of vasopressor but not simply
because of a direct mechanistic principle. Other factors are implicated; there is
evidence that several shared key components of IR are activated in major bleeding
[26] and in vasoplegia after CPB. [16]. Therefore, we may consider that the use of a vasopressor does not depend exclusively
on the amount of bleeding. We believe that TA could attenuate inflammatory changes
through blockade of fibrinolysis and may modulate interactions between the different
systems involved in the global response to CPB [1].

Limitations of the study

Even though greater postoperative bleeding was associated with IR after CPB, a limitation
was the failure to determine fibrinolysis parameters in the first part of the study.
The main limitation of part 2 of the study is the sample size. However, this was a
randomized controlled study and baseline data were comparable between groups. Additionally,
although inclusion of patients was prematurely stopped, data analysis demonstrated
that TA attenuates IR in patients after CPB. This small sample size could lead to
a type II error regarding secondary endpoints, such as durations of hospital stay
and ICU stay.

Conclusion

The use of TA attenuates the development of IR and VS after CPB, with hyperfibrinolysis
playing a predominant role in their development.

Key messages

• Hyperfibrinolysis may play a role in inflammatory response (IR) after cardiopulmonary
bypass (CPB).

• Inhibition of fibrinolysis with tranexamic acid may attenuate IR after CPB.

Competing interests

The authors declare that they have no competing interests.

Authors' contributions

JJJ and JLI were responsible for the study design, data collection, processing blood
samples during the study, statistical analysis, data interpretation, and drafting
the manuscript. LL, RP, MB, and MLM were responsible for data collection and processing
blood simples during the study and provided useful suggestions. JMR was responsible
for determination of coagulation-fibrinolysis parameters and interpretation. IN and
RM were the surgical team and were responsible for preoperative clinical and analytical
data collection. AM was responsible for the determination of complement, leptins,
soluble tumor necrosis factor receptors, interleukin-6, and interpretation. DH was
responsible for the statistical analysis, data interpretation, and drafting the manuscript.
All authors read and approved the final manuscript.

Acknowledgements

The authors thank the staff of the Intensive Medicine Unit and Hematology Department
(Hospital Universitario de Canarias, La Laguna, Spain) for their invaluable collaboration
in this study. This study was supported by FUNCIS (Fundación Canaria de Investigación
y Salud) 2202.